Integrated bound-mode spectral/angular sensors

ABSTRACT

A 2-D sensor array includes a semiconductor substrate and a plurality of pixels disposed on the semiconductor substrate. Each pixel includes a coupling region and a junction region, and a slab waveguide structure disposed on the semiconductor substrate and extending from the coupling region to the region. The slab waveguide includes a confinement layer disposed between a first cladding layer and a second cladding layer. The first cladding and the second cladding each have a refractive index that is lower than a refractive index of the confinement layer. Each pixel also includes a coupling structure disposed in the coupling region and within the slab waveguide. The coupling structure includes two materials having different indices of refraction arranged as a grating defined by a grating period. The junction region comprises a p-n junction in communication with electrical contacts for biasing and collection of carriers resulting from absorption of incident radiation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 15/706,440 filed Sep. 15, 2017 (now allowed) whichis a continuation application of U.S. patent application Ser. No.15/317,592 filed Dec. 9, 2016 (now allowed) which claims priority to PCTPatent Application No. PCT/US2015/34868 filed on Jun. 9, 2015, whichclaims priority to U.S. Provisional Patent Application Ser. No.62/009,832, filed Jun. 9, 2014 and to U.S. Provisional PatentApplication Ser. No. 62/099,981, filed Jan. 5, 2015, the entireties ofwhich are incorporated herein by reference.

GOVERNMENT SUPPORT STATEMENT

This invention was made with government support under Grant No.EEC0812056 awarded by the National Science Foundation. The governmenthas certain rights in the invention.

FIELD OF THE INVENTION

This invention relates generally to the field of lighting, particularlysmart lighting comprising sensors, and specifically to the field ofintegrated bound-mode spectral/angular sensors.

BACKGROUND OF THE INVENTION

The ongoing conversion of indoor lighting to energy efficient LEDsystems offers enormous opportunity for increasing the functionality oflighting from today's modest on/off/dimming control to a new SmartLighting paradigm that takes advantage of LEDs' electronic compatibilityand flexibility. This new lighting paradigm includes lighting forenhanced worker/student productivity, health effects such as circadianentrainment reinforcing the human sleep/wake cycle, visible lightcommunications (VLC) to alleviate the growing wireless bottleneck, andoccupancy/activity sensing to provide custom lighting.

The highest lighting efficacy will be achieved with multiple LEDs atdifferent colors across the visible, eliminating the energy lossesinherent in phosphor color conversion. VLC will require a multiple-inputmultiple-output (MIMO) architecture with multiple LEDs from multiplefixtures to provide the necessary aggregate Gbps data rates and tosupport mobility as people move with their personal devices. Light hasmany impacts on health and productivity; spectral as well as intensityvariations are important for optimizing the human environment. An evengreater energy savings, along with a more comfortable experience, isavailable by adapting lighting to human activity in addition to thesavings from the improved efficacy of LEDs.

Currently there is a trend to develop smart lighting that involvesmultiple LEDs in each light fixture with 4 to 10 independent colorsspanning the 400-nm to 700-nm visible spectrum. There is a need in theart to provide smart lighting that will allow a broad color gamut, butalso require a sophisticated control system to adapt to differentlighting conditions, different impacts of furnishings and walls, floors,ceilings, and/or different aging of the LEDs in different fixtures.While today's color cameras include components, such as photosensitivepixels that could be integrated for use in smart lighting, the angularand spectral resolution requirements needed for smart lighting sensorsare quite different than those of traditional cameras that requireangular insensitivity and only have pixels with three relativelybroad-band and spectrally overlapped color filters (RGB). Most commonly,today's color cameras utilize dye absorbers, typically with spectralbandwidths of ˜100 nm or greater that are located directly atop thesilicon photosensitive pixels of the camera.

Attempts at developing technology for smart lighting components includefocal plane color filters for application to the color pixels of digitalcameras. Surface plasma wave (SPW) enhancement of semiconductordetectors has been extensively investigated in the infrared spectralregion. Typically, in the IR the approach is to couple to a SPW bound tothe metal-semiconductor interface. This allows the use of a thinnerabsorption region (with, therefore, lower noise currents) and a longerabsorption path (along the pixel rather than across the junction depth).However, this approach is not appropriate for the visible spectrum dueto the high, and strongly varying, absorption of silicon across thevisible spectrum. Another issue is the small scale of the requiredgrating which is ˜λ/n with n, the semiconductor refractive index, of 4to 5 for silicon across the visible spectrum. Additionally, limitationsof the SPW approach include: 1) the relatively high metal optical lossesin the visible restrict the available bandwidths; spectral widths aretypically 100 to 200 nm, an order of magnitude larger than the desiredbandwidths; and 2) the transmission is low, typically no larger than10%, limiting the sensitivity of the measurement.

While there have been many demonstrations of far-field filtering (planewave to plane wave), relatively few demonstrations of coupling tosilicon materials for detection have been presented. In such fewdemonstrations, linewidths have been broad, typically 100 to 200 nm. Theterm “plasmonics” generally covers both extended (propagating) surfaceplasma waves (SPW) defined on a metal-dielectric interface and localizedsurface plasma resonances (SPR) associated with metal particles, holesin a metal film, discs of metal, etc. The angular responses SPW's andSPR's are quite different with SPW's having a narrow angular responsedepending on the periodicity of the surface while SPR's have generallyangularly independent responses. In any real plasmonic structure thesetwo resonances interact giving a complex, wavelength dependent angularresponse. Meanwhile, pixels are generally small, driven by trends inhigh-pixel count cameras where individual pixels are sub-10 microns.Further, many studies have demonstrated a far-field filter approachbased on extraordinary optical transmission through arrays of holes in ametal film where the far-field transmission of the filter is used as thespectrally selective quantity. That approach is difficult to achieve ina convenient form factor as a result of the long propagation distancesrequired to achieve a far field regime, requiring standoff of the filterelement from the silicon detector array.

Other work has focused on radiation coupling with a 2D waveguidefabricated on a substrate. For example, guided-mode resonance (GMR)filters, consisting of a grating coupler and a single mode slabwaveguide on a transparent substrate have demonstrated both angular andspectral sensitivity in reflection and transmission. Off-resonance, GMRfilters simply act as a dielectric medium, usually with the majority ofthe incident power simply being transmitted. On resonance, the gratingcouples some of incident photons into the waveguide and the propagatingphotons in the waveguide are coupled back into the reflected andtransmitted beams. As a result of the phase shifts inherent in thisprocess, the out-coupled photons reinforce the reflected wave andinterfere destructively with the directly transmitted light to reducethe transmitted power. Since the waveguide is lossless and the gratingis large (many wavelengths), an extremely narrow resonance response isachieved.

Waveguide integrated optics at telecommunications wavelengths hasdemonstrated that grating coupling into waveguide modes can provide thenecessary spectral and angular filtering with recent demonstrations ofonly 0.6 dB loss in conversion from a 2D waveguide to a single modefiber.

What is needed in the art is a device that comprises color pixels withboth color and angular sensitivity that can be integrated onto a siliconsurface with a scalable, manufacturable process (e.g., not requiringseparate fabrication steps for each desired wavelength/angle setting),providing both manufacturing convenience and reduced form factors.

Further, the silicon absorption varies considerably across the visible.At blue wavelengths (about 400 nm) the absorption of silicon is quitestrong with a 1/e absorption length of only ˜100 nm. In contrast at thered end of the spectrum (about 700 nm) the silicon 1/e absorption lengthis ˜8 micrometers (80× longer). As a consequence, the responsivity ofsilicon photodetectors also varies across the visible. For bluesensitivity, the junction depth must be quite shallow, within the short1/e absorption length, which is difficult to accomplish with traditionalCMOS fabrication processes. Therefore, another aim of the invention isto provide a CMOS compatible p-n junction technology that accommodatesthe short penetration depth of blue photons into silicon.

SUMMARY

Some embodiments described herein use grating coupling to bound modespropagating on a metal, which can be coated with a protective layer ofsilica, and a photon that tunnels through the metal to an underlyingsilicon p-n junction, for example, a fabricated silicon wafer. Someembodiments described herein use grating coupling to bound modespropagating along the surface of a silicon wafer. These may be surfaceplasma waves bound to a metal/dielectric interface, or waveguide modesconfined by a dielectric stack (typically low index cladding, high indexconfinement layer, and low index cladding).

In an embodiment, there is a 2-D sensor array. The 2-D sensor arrayincludes a semiconductor substrate, and a plurality of pixels disposedon the semiconductor substrate. Each of the plurality of pixels includesat least one coupling region and at least one junction region, and aslab waveguide structure disposed on the semiconductor substrate andextending from the at least one coupling region to the at least onejunction region. The slab waveguide includes a confinement layerdisposed between a first cladding layer and a second cladding layer. Thefirst cladding and the second cladding each have a refractive index thatis lower than a refractive index of the confinement layer. Each of theplurality of pixels also includes at least one coupling structuredisposed in the coupling region and within the slab waveguide. Thecoupling structure includes at least two materials having differentindices of refraction, and arranged as a grating defined by a gratingperiod. The junction region comprises a p-n junction in communicationwith electrical contacts for biasing and collection of carriersresulting from absorption of incident radiation.

In another embodiment there is a 2-D sensor array. The 2-D sensor arraycomprises a plurality of pixels including at least a first pixel and asecond pixel. Each of the first and second pixels include a slabwaveguide portion, a single mode waveguide portion, an adiabatic taperportion for funneling incident light from the slab waveguide portioninto the single mode waveguide portion, and a plurality of resonantadd-drop filters formed substantially adjacent to the single modewaveguide portion. The slab waveguide comprises a confinement layerdisposed between a first cladding layer and a second cladding layer,wherein the first cladding and the second cladding each have arefractive index that is lower than a refractive index of theconfinement layer, and a grating disposed in the first cladding layerfor coupling incident light into the slab waveguide. The first pixel'sgrating has a first grating period and the second pixel's grating has asecond grating period.

In another embodiment there is a CMOS-compatible photodetector. TheCMOS-compatible photodetector comprises a first semiconductor layerdoped with a first carrier type and a second semiconductor layer dopedwith a second carrier type. The first semiconductor layer comprises aplurality of posts. The second semiconductor layer is configured with aplurality of holes extending through the second semiconductor layer. Atleast one of the posts extends through a corresponding one of theplurality of holes in a honeycomb pattern. The honeycomb patterncomprises a plurality of edge portions, each of the plurality of edgeportions comprising a respective one of a depletion region area.

In another embodiment there is a method of detecting electromagneticradiation. The method includes providing a 2-D sensor array. The 2-Dsensor array comprises: a semiconductor substrate comprising a pluralityof pixels. Each of the plurality of pixels comprises at least onecoupling region and at least one junction region, a slab waveguidestructure disposed on the semiconductor substrate and extending from thecoupling region to the junction region, and a localized semiconductorlayer forming at least one p-n junction with the semiconductor substratein the junction region. The slab waveguide comprises: a confinementlayer disposed between a first cladding layer and a second claddinglayer, wherein the first cladding and the second cladding each have arefractive index that is lower than a refractive index of theconfinement layer. The pixels further comprise at least one gratingdisposed in the slab waveguide. The at least one grating comprises agrating period. The method also includes coupling incoming light intothe slab waveguide at the coupling region, propagating the light to theregion over the junction area, decoupling the light such that it entersthe junction region, and converting the light into at least oneelectron-hole pair, wherein the incoming light comprises at least onemodulated waveform.

Advantages of the embodiments will be set forth in part in thedescription which follows, and in part will be understood from thedescription, or may be learned by practice of the invention. Theadvantages will be realized and attained by means of the elements andcombinations particularly pointed out in the appended claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description, serve to explain the principles of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of elements of a CMOS compatibleintegrated plasmonic detector.

FIGS. 2A-2B are images showing different scanning electron micrograph(SEM) views of exemplary 2D gratings on the top of a plasmonicstructure.

FIG. 3 is a side, cross-sectional view of an exemplary implementation ofa mechanical light aperture on the top of a plasmonic structure usinginterconnect layers.

FIG. 4 is a cross-sectional view of an exemplary implementation ofwavelength resonant structures placed between a plasmonic device and aphotodetector.

FIGS. 5A-5B show a sensor comprising a dense array of photodetectors(FIG. 5A) that are accessed electronically via an on-chip circuitryshown as a block diagram (FIG. 5B).

FIG. 6A is perspective view of an integrated waveguide enhanced CMOScompatible plenoptic detector element according to an embodiment.

FIG. 6B is an optical micrograph image of a fabricated integratedwaveguide enhanced CMOS compatible plenoptic detector element accordingto the structure shown in FIG. 6A. The insets are SEM images of thegratings in the coupling and detection regions.

FIG. 6C is a perspective view of another embodiment of an integratedsensor detector element.

FIGS. 7A-7B illustrate a side cross-sectional view (FIG. 7A) and a topview (FIG. 7B) of a waveguide filter of an embodiment.

FIGS. 8A-8B illustrate a side cross-sectional view (FIG. 8A) and a topview (FIG. 8B) of a waveguide filter of an embodiment.

FIG. 9 is a top view of a waveguide filter of an embodiment andillustrates the use of a chirped grating to adjust the bandwidth of thedetected light in an integrated sensor detector element.

FIG. 10A is a top view of a waveguide filter of an embodiment andillustrates the use of a curved grating (FIG. 10A) and a smallerdetector element.

FIG. 10B is a top view of a waveguide filter of an embodiment andillustrates a combined chirped and curved grating coupler.

FIG. 11 is a top view of a waveguide filter of an embodiment andillustrates the use of more complex grating couplers in an integratedsensor detector element comprising a single coupling area with multiplejunction areas.

FIGS. 12A-12B are each top views of respective a waveguide filter of anembodiment and each further illustrate the use of more complex gratingcouplers to extend the functionality to multiple wavelengths with acombined coupling area.

FIG. 13 illustrates an embodiment comprising a slab waveguide that istapered on an end to a single mode guide that includes add-drop filtersbased on circular resonant whispering gallery structures for isolatingvarious spectral regions.

FIG. 14A is a graph showing experimentally obtained angular resolutionof a single grating coupled waveguide detector for RGB laser sources ofdifferent wavelengths (652.3 nm, 532.2 nm and 407.8 nm). The expandedviews show results for the TE (solid) and TM (dotted) experiments(circles) and simulations (dash-dot).

FIG. 14B is a graph showing experimentally obtained angular resolutionof a single grating coupled waveguide detector for RGB laser sources.The bottom panel shows the results with the same waveguide with gratingperiods of 320- and 380-nm. The 320-nm grating results are expanded inthe top panels and compared with simulation curves (shown as thickercurves).

FIG. 14C-14D are graphs showing the angular spectral response for aparticular implementation with the grating period as a parameter.

FIG. 15 is a graph showing the ideal (fundamental limit, unity quantumefficiency) and actual responsivities of an ideal photo-detector and acommercial photo-detector, respectively.

FIG. 16 is a graph showing measured responsivity (photocurrent) versusposition of a laser beam on a fabricated photodetector.

FIGS. 17A-17C illustrate a top view (FIG. 17A), a cross-sectional areaof a first portion (FIG. 17B) and a cross-sectional area of a secondportion (FIG. 17B) of a planar p-n detector. The substrate (p-) contactis not shown.

FIG. 18A-C is a top view (FIG. 18A), a cross-sectional view of a firstportion (FIG. 18B) and a cross-sectional area of a second portion (FIG.18C) of a CMOS-compatible honeycomb p-n detector of an embodiment.

FIG. 19A is a graph showing spectral response data for detectors havinga honeycomb p-n junction device of an embodiment versus a planar p-njunction of a typical detector.

FIG. 19B is a graph showing photocurrent improvement achieved by thehoneycomb structure.

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the present embodiments,examples of which are illustrated in the accompanying drawings. Whereverpossible, the same reference numbers will be used throughout thedrawings to refer to the same or like parts.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements. Moreover, all ranges disclosed hereinare to be understood to encompass any and all sub-ranges subsumedtherein. For example, a range of “less than 10” can include any and allsub-ranges between (and including) the minimum value of zero and themaximum value of 10, that is, any and all sub-ranges having a minimumvalue of equal to or greater than zero and a maximum value of equal toor less than 10, e.g., 1 to 5. In certain cases, the numerical values asstated for the parameter can take on negative values. In this case, theexample value of range stated as “less that 10” can assume negativevalues, e.g. −1, −2, −3, −10, −20, −30, etc.

The following embodiments are described for illustrative purposes onlywith reference to the Figures. Those of skill in the art will appreciatethat the following description is exemplary in nature, and that variousmodifications to the parameters set forth herein could be made withoutdeparting from the scope of the present invention. It is intended thatthe specification and examples be considered as examples only. Thevarious embodiments are not necessarily mutually exclusive, as someembodiments can be combined with one or more other embodiments to formnew embodiments.

A CMOS-compatible plenoptic (angle and wavelength) detector for LEDlighting applications is described herein. In some embodiments, theplenoptic sensor has both spectral (≲30 nm) and angular (100 mrad; 5°)resolution. Furthermore, such a sensor may be based on a scalablesilicon IC platform to meet mass-market cost targets, may have a lowprofile for broad installation flexibility, and does not have any movingparts such as a grating rotation for manufacturing and operationalsimplicity and robustness.

Described herein are embodiments of a plenoptic sensor waveguidedetector element. The detector element of the embodiments may beincorporated in one or more pixels such as a 2-D pixel array which maybe included in CMOS-compatible photodetector. In such embodiments,grating coupling is used to bound modes propagating along the surface ofthe silicon wafer. The bound modes may be surface plasma waves bound toa metal/dielectric interface as in sensor elements 100, 300 and 400shown in FIG. 1, or waveguide modes confined by a dielectric stack(typically low index cladding, high index confinement layer, and lowindex cladding) as in sensors element 600 of FIG. 6A, sensor element600′ of FIG. 6C, sensor element 700 of FIG. 7A, and sensor element 800of FIG. 8A.

In either case the phase matching condition for coupling is given byequation (1):

$\begin{matrix}{{{\frac{2\;\pi\;\sin\;\theta_{in}}{\lambda_{in}} + {j\;\frac{2\pi}{d}}} = {\pm {k_{{mod}\; e}\left( \lambda_{in} \right)}}},} & (1)\end{matrix}$where θ_(in) is the angle of incidence (−1<sin θ_(in)<1), j is aninteger (±1, ±2, . . . ), λ_(in) is the optical wavelength, d is thegrating period; and k_(mode)(λ_(in)) is the modal wave vector typicallygiven by a dispersion relation that takes into account the waveguidestructure and the incident wavelength.

If light is incident at varying angles as it is, for example, for asensor mounted on a wall where light comes directly from multipleluminaires (i.e., separated and extended light sources such as lightbulbs or LEDs) and also from multiple bounces around the room, accordingto coupling equation (1) light at different angles is coupled in atdifferent wavelengths. That is, the coupling equation (1) depends bothon the angle of incidence and the wavelength. This problem must beresolved to provide a sensor output of spectrum vs. angle of incidence.Since the goal is the spectrum as a function on angle of incidence, thisdependence is desired. However, it is necessary to deconvolve the twoaxes from the measurement. Thus, two measurement axes are required toseparate out the two dependencies. One measurement axis is provided byvarying the period of the grating on adjacent pixels. The secondmeasurement axis requires either: a) a blind structure above thedetector active surface to control the angle of incidence, or b) aresonant frequency measurement structure (similar to a series ofresonant add-drop filters along the waveguide) to separate out thespectrum. Thus, by fixing one axis directly, for example, either theangle (in the case of the blinds) or wavelength (in the case of theresonant filters) as a measured signal, the other axis can be deducedfrom the measured signal. In the case of the blind structure, there is apart that sets the angle, and the received color is then a function ofthe grating pitch. In the case of the waveguide structure, there is apart that provides a convolution of angle and wavelength (correspondingto sin θ/λ) and then a series of resonant add-drop filters that providewavelength information.

For electronically controllable LEDs, each color can have a uniqueelectronic signature that can encode the color eliminating the need fordirect wavelength measurement. That is, the signals can be separatedelectronically. This electronic coding can be at a frequency well abovehuman perception, so it has no impact on the lighting functionality.

Surface Plasma Wave Spectral/Angular Detection

In one set of embodiments, the spectral/angular separation isaccomplished with a plasmonic guiding structure atop the silicondetector. As long as Re(ε_(d)+ε_(m))<0, a metal film supports a surfaceplasma waves (SPW) associated with the metal/dielectric interface oneach side of the metal film. The SPE is a bound mode that propagatesalong the interface and decays exponentially into both the metal and thedielectric.

For a Ag/SiO₂ interface this condition is satisfied across the visible.For a Ag/Si interface this condition is violated at the blue end of thespectrum, so that the SPW does not exist across the entire visible. Thusin this set of embodiments, the coupling is to the upper Ag/dielectricinterface. For a sufficiently thin metal, there the SPW also mediatesthe transmission through the metal leading to a spectral/angularresponse at the underlying p-n junction.

As shown in FIG. 1, in some embodiments, a plenoptic sensor element 100may comprise a semiconductor substrate 111. A surface plasma wavesupporting structure 113, a grating coupler 115 and a photodetector 117may each be disposed over the sensor element 100. The substrate may be asilicon substrate, for example a p-type silicon substrate. While some ofthe embodiments described herein include a p-substrate with ann-diffusion to create the junction area, other configurations arepossible. For example, embodiments described herein may instead includen-substrate used with a p-diffusion to create the junction. Thephotodetector may include a thin n-type diffusion layer 119 incorporatedin the substrate 111. The plasmonic structure 113 may be formed with aplasmonic layer 123 which may comprise a metal disposed over thesubstrate 111. In certain embodiments, the plasmonic layer 123 may be athin continuous metal sheet which minimizes the required manufacturingsteps and, therefore, production cost. The plasmonic layer 123 maycomprise aluminum which provides the best known plasmonic performance inblue light region.

In certain embodiments a protection layer 125 can be added between theplasmonic layer 123 and the grating 115. The protection layer 125protects the plasmonic layer 123 from airborne contamination anddeteriorating substances. The protection layer may comprise aluminawhich may be deposited using evaporation, laser or e-beam ablation oratomic layer deposition (ALD) techniques.

In certain embodiments a spacer layer 121 with low refraction index canbe added as a spacer between a metal sheet of the plasmonic layer andthe registering device. Such a spacer benefits spectral response(selectivity) of the device by substantial attenuation of evanescentfields caused by zero- and all higher orders except for the lightcoupled into plasmons which exhibit leaky mode behavior. In anembodiment, the low-index dielectric layer 125 may comprise Al₂O₃,and/or the spacer layer 121 may comprise SiO₂.

A grating can be disposed over the plasmonic layer 123 for coupling oflight into the surface plasmons. In certain embodiments a plurality ofperiodic structures 127, such as a plurality of Si/Air periodicstructures, can be used as a coupling grating 115. Such a couplinggrating has one of the highest refractive index contrasts available inthe visible light range thus providing high coupling efficiency whileretaining high compatibility with CMOS processing. In certainembodiments a coupling grating can be implemented as a high permittivityelement 129 (semiconductor or metal) placed on top of a low refractiveindex spacer element 131, such as a dielectric, which may be SiO₂. Sucha combination of high permittivity element 129 with low refractive indexspacer element 131 provides for high grating coupling efficiencyconnected with reduced effective refractive index of surrounding mediawithin plasmonic evanescent field. This allows having the same filteringwindow with a larger grating pitch thus easing fabrication. In certainembodiments a 1D coupling grating can be used to incorporatepolarization sensitivity to the plenoptic sensor. In certain embodiments2D square (FIGS. 2A-2B) or 2D hex-patterned (not shown) coupling gratingcan be used for enabling polarization insensitive operation.

Returning to FIG. 1, a period of the grating 115, for example, theperiod of the periodic structure 127 can be approximately λ/n_(d), wheren_(d) is the index of the dielectric. The surface plasmon at thesilicon/metal interface is not well defined since the dielectricconstant (ε) of the silicon (ε=16 to ε=25 across the visible) is largerthan the magnitude of the real part of the metal (ε˜10). Instead,embodiments couple to a plasmon on the other side of the plasmonic layer123 (which may coated with a protective spacer layer 121 of silica,ε˜2.25) and tunnel the photon through the thin metal to the underlyingsilicon. In other words, the plenoptic sensors element 100 can providecoupling to the (low-index) dielectric 125 above a plasmonic layer 123and transmission through the plasmonic layer 123 to the underlyingsemiconductor.

The sensor element 100 may further include a surface plasma wave (SPW)contact 112 that contacts at least the plasmonic layer 123 and ann-contact 114 that contacts the n-type diffusion layer 119. The sensorelement 100 may further include a p-contact (not visible in FIG. 1).

As discussed above, an additional filtering structure 333 can be used toresolve angular-wavelength degeneracy of the plasmonic filteringstructure as illustrated in FIG. 3. For example, in certain embodimentsmechanical light apertures 335, 335′ can be used as additional filteringstructure disposed over device 100 as shown in FIG. 3. The mechanicallight aperture reduces the angular spread of the light 340 incident on aparticular device element, thus eliminating the degeneracy.

In certain embodiments at least one of a wavelength resonant structure412, as shown in FIG. 4, can be incorporated in a plenoptic sensorelement 400. The wavelength resonant structure 412 may be added toelement 100 as described below. For example, an additional filteringstructure may be placed between the plasmonic layer 123 andphoto-detector 117, thereby modifying element 100 of FIG. 1 as element100′ as shown in FIG. 4. The wavelength resonant structure 412 mayinclude alternating dielectric layers 414, 416, and 418, and may furtherincorporate layer 121. Together the alternating dielectric layers 414,416, 418 and 121 are configured as several Fabry-Perot resonators withdifferent free-spectral ranges and center frequencies designed in such away that only a particular bandwidth of continuum is passed through thuseliminating the degeneracy.

In certain embodiments a complete sensor consists of an array ofwavelength/angular p-n-junction photodetectors that are accessed usingon-chip electronics. An example of such array is shown on FIG. 5A. Thearray comprises a plurality of pixels, with each pixel comprising arespective one of plenoptic sensor element 100, 300 or 400 describedabove.

The plasmonic structure can comprise a continuous metal sheet formedbetween a protective layer, such as a first dielectric layer, and asecond dielectric layer, wherein the continuous metal sheet comprisessilver. The angular filtering structure comprises a mechanical lightaperture for reducing angular spread of the incident light and reducingdegeneracy. The plasmonic structure can further comprise a grateddielectric layer formed on the first dielectric layer. The grateddielectric layer and the second dielectric layer can each comprise SiO₂and/or the first dielectric layer can comprise Al₂O₃. The couplinggrating can comprise a grated semiconductor/air periodic structure. Thecoupling grating can comprise a high permittivity element selected froma semiconductor or a metal disposed on a low refractive index spacer,wherein the high permittivity element can comprise a higher permittivitythan the low refractive index spacer. The coupling grating can comprisea 1-D coupling grating, a 2D square coupling grating, or a 2Dhex-patterned coupling grating. Each of the first and second pixels canfurther comprise a photodetector and a wavelength resonant filteringstructure, wherein the wavelength resonant filtering structure isdisposed between the plasmonic structure and the photodetector. Thewavelength resonant structure can comprise a plurality of Fabry-Perotresonators, each with a corresponding free-spectral range and centerfrequency, wherein the Fabry-Perot resonators can be configured to allowonly passage of a predetermined bandwidth of light continuum through theplasmonic device. The pixels of the 2-D array sensor can be inelectrical communication with on-chip electronics or it can be bonded toa readout integrated circuit (ROIC) as shown in FIG. 5B. The 2-D arraycan further comprise a semiconductor substrate and a plurality of p-njunctions. The plurality of pixels may be disposed on the semiconductorsubstrate.

Dielectric Waveguide Spectral/Angular Detection

All dielectric-confined guided modes offer a lower loss alternative tometal-dielectric SPWs. Thus, in an embodiment there is providedwaveguide coupling into waveguide modes for spectral and angularfiltering to the visible spectrum, using lossless waveguides integratedwith CMOS-compatible Si photodetectors. Plenoptic sensors comprisingwaveguides as described herein easily meet the spectral and angularresolution requirements described above, are readily scalable to arrayarchitectures, and easily will provide the RF bandwidths and out-of-bandrejection required for visible light communications, VLC.

To retain the CMOS compatibility, a plenoptic sensor element 600 in FIG.6A may include a three layer waveguide structure 613. The waveguidestructure 613 may include a first low index cladding layer 621, a highindex confinement layer 623, and a second low index cladding layer 625(e.g., a SiO₂/Si₃N₄/SiO₂ waveguide) disposed over a substrate 611, whichmay be a silicon substrate. The first low index cladding layer 621 andthe second low index cladding layer 625 may each comprise Sift. The highindex confinement layer 623 may comprise Si₃N₄. The refractive indicesof the waveguide layers include are: SiO₂−1.5, Si₃N₄˜2.2. The layers ofthe waveguide structure may be transparent across the visible spectrum.One of ordinary skill will understand that other material combinationsfor the waveguide layers are available and are included herein withoutexplicit reference.

In operation, incident light 640 is coupled to the waveguide 613 at aspecific wavelength and incident angle at a coupling region 640′,providing a spectral/angular filtering function. The incident light iscoupled into the waveguide 613 by a grating coupler 615 located at acoupling region 640′. The grating coupler 615 comprises a plurality ofdielectric grates 627. The light is then out-coupled from the waveguide613 downstream from the coupling region at an out-coupling grating 615′located at junction region 640″ to a photodetector 617 fabricated in theunderlying silicon substrate 611 and comprising at least one p-njunction. A second grating at a junction area 615′ is used to out-couplethe light into the semiconductor detection region of the photodetector.Thus, the thickness of the first low index cladding layer 621 should beselected to ensure that the fields do not extend significantly into theabsorptive silicon substrate 611, the thickness of the confinement layer623 should be selected to assure single mode in the depositiondirection, and a thickness of the second low index cladding layer 625should be selected to control the coupling strength.

The p-n junction is first defined with an appropriate doping profile.Since the active areas are quite large, one alternative is to use asimple diffusion process to define the junction areas. Alternatively,ion-implantation and annealing can be used as is well known in the art.Following the junction formation, blanket layers of the waveguide—lowercladding, waveguide core, and upper cladding—are deposited by anappropriate deposition technique. Techniques such as sputtering,evaporation and spin coating among others are available and arewell-known. One or more lithography and pattern transfer steps are nextused to define the in-coupling and out-coupling regions. Additionalstandard lithography/etch/metal deposition/annealing steps are used toprovide the electrical contacts and the cover over the p-n junction toprotect it from direct illumination.

As shown in FIG. 6C, an alternate structure of an integrated plenopticsensor element 600 includes a waveguide 613 as well as a first grating627 and a second grating 628. With a cover 628′ over a detector area,such as over a portion of second grating 615′, to eliminate directillumination of the detector element. Cover 628′ may be an opaquematerial, for example a metal thicker than ˜100 nm. A separation layer(not shown) may be necessary depending on the thickness of the uppercladding and the etch depth of the coupler.

In an example, the photodetector 617 may comprise an n-doped region 619of the substrate 611 which may be a p-type substrate. A plenoptic sensorwill require an array of pixels comprising such detection elements, atleast two of the elements having different pitch or orientationgratings. A grating coupler 615 along with the single mode slabwaveguide 613 provides the necessary angular/wavelength selectivity asis evident from the coupling equation (1) described above.

The parameters of the waveguide are chosen to provide a single (TE, TM)mode pair across the visible allowing the use of different gratings toadjust the individual pixel angular/wavelength coupling resonances.

In a single mode slab waveguide, the modal index of this slab variesacross the range of 1.5 (at long wavelengths, e.g. the refractive indexof the cladding) to 2.2 (at short wavelengths, e.g. the refractive indexof the core). Without the grating, there is no coupling for lightincident on this waveguide from the top since the mode phase velocity isalways slower than the speed of light in free space. Just as in the SPWcase, this momentum deficit can be made up with a grating. Very highcoupling efficiencies, approaching 100%, are readily achieved. Since thewaveguides are lossless, the resonance line widths are much smaller thanin the SPW case. The measured linewidth is a function of: 1) the widthof the grating; 2) the illuminated grating width; and 3) the gratingcoupling strength. As illustrated below, with an illuminated gratingwidth of 200 μm in the weak coupling limit, a resolution of ˜5 nm wasachieved with a 200 μm wide coupling area. It is possible to adjust theresonance linewidths by several techniques: 1) chirping (varying thepitch across the collection area) the grating, and 2) including a lossyelement, for example but not restricted to silicon nanoparticles in thewaveguide to increase the waveguide losses. It will be necessary todesign an appropriate engineering compromise between the resonancebandwidth and the propagation lengths between the coupling region andthe detection region.

In one implementation of a plenoptic sensor element shown in FIGS.7A-7B, incident light 740 is coupled into a slab waveguide 713 by afirst dielectric coupling grating 727 located at a coupling area 740′.As the light propagates under a metal block 714, which is placed toshield the p-n junction between n-type portion 719 of the p-typesubstrate 711, a second out-coupling grating 727′ located at a junctionarea 740″, out-couples the light into the semiconductor detection region717. As shown, the coupling constant is higher (e.g., the grating teethare deeper) so that the out-coupling occurs in a shorter distancerelative to the coupling grating 727. In FIG. 7B, a top view shows twopixels, each pixel comprising one of sensor element 700 and shown as700-1 and 700-2. Each pixel is shown having a respective one of gratingperiods, p1 and p2, wherein the grating period p1 of pixel 700-1 isdifferent than the grating period p2 of pixel 700-2.

In another implementation shown in FIG. 8A, instead of having a second(out-coupling) grating such as second grating 727′ of element 700,element 800 includes a pedestal portion 828 at a junction area 740″.However, element 800 still includes a first grating 815 at a couplingarea 740′. The pedestal portion 828, also located at the junction area740″ extends from the substrate so that the evanescent field from thelower index cladding layer 721 reaches the higher index silicon. Thatis, the out-coupling grating is replaced by a leaky mode outcouplingbased on bringing the silicon p-n junction between n-type portion 719and p-type substrate 711 into the cladding 721. Thus, in this leaky-modegeometry, the field will couple to radiative modes in the silicon and asignal will be detected. Manufacturing details will be important indeciding between these out-coupling alternatives. In FIG. 8B, a top viewshows two pixels, each pixel comprising one of sensor element 800 andshown as 800-1 and 800-2. Each pixel is shown having a respective one ofgrating periods similar to the grating periods p₁ and p₂ of FIG. 7B,wherein the grating period p₁ is different than the grating period p₂.

The waveguide approaches described for the elements of FIGS. 7A-7B and8A-8B have the same convolution of angular and spectral responses as theSPW approaches of the embodiments described above. Accordingly, theapproaches presented above with respect to FIGS. 4 and 5A-5B can also beapplied in the waveguide embodiments of FIGS. 6A-8B.

For a SiO₂/Si₃N₄/SiO₂ waveguide, the modal index of the slab waveguidecan be between about 1.5 to about 2.2. The dielectric grating cancomprise a first dielectric grating and the slab waveguide can furthercomprises a second dielectric grating disposed between the metal blockand the semiconductor layer. The second dielectric grating can comprisea coupling constant that is higher than that of the first dielectricgrating such that the second dielectric grating out-couples light into adetection region. The plurality of out-coupling gratings of the seconddielectric grating can have a coupling strength greater than thecoupling strength of the first plurality of gratings, thereby achievinga concentration of the optical signal. Each of the first and the seconddielectric gratings can comprise a plurality of grating teeth, and thesecond dielectric grating's teeth can be thicker than the firstdielectric grating's teeth. The first grating period can be differentthan the second grating period. A portion of the substrate disposedunder the metal block can comprise a raised portion that extends the p-njunction into the first cladding layer.

In an embodiment, the p-n junction of the device described in FIGS.8A-8B can be replaced by an interdigitated Schottky barrier (notillustrated) without requiring any doping. The fingers of the Schottkybarrier contacts can also serve as the outcoupling grating.

As discussed above the bandwidth of the spectral selectivity for a fixedangle of incidence can be adjusted by changing the pitch of the couplinggrating across the coupling region. This is illustrated in FIG. 9 whichshows a top view of a sensor element 900 that is similar to sensorelement 600′ of FIG. 6C is illustrated. The sensor element 900 comprisesa chirped grating 915 with a variable pitch across the coupling regionand an out-coupling grating 915′ in the junction region which may befixed or chirped. For simplicity of representation, the top cover thatprevents direct illumination of the junction area (e.g., 714 in FIG. 8A)is not shown in FIGS. 9-12B. The chirped grating 915 will be importantin adjusting the spectral resolution for specific applications. Inparticular, typical light emitting diodes (LEDs) have bandwidths of ˜20-to 40-nm, to assure appropriate coverage it is best to set theresolution of the measurement to ˜20 nm.

The coupling grating is not constrained to straight line segments. Forexample, in FIG. 10A, a top view of sensor element 1000 that is similarto sensor element 600′ of FIG. 6C is shown. Sensor element 1000comprises curved grating 1015 in the coupling region 1040′ includes aset of curved grating segments. The curved grating 1015 serves to focusincoming light within the 2D waveguide slab (e.g., 613) to allow asmaller active junction area 1040″ where outcoupling grating 1015′ islocated. This has advantages in terms of reduced areal space usage, interms of reduced detector dark noise, and in terms of increase detectorspeed (reduced capacitance). In FIG. 10B, a sensor element 1000′ that issimilar to sensor element 600′ of FIG. 6C comprises a grating 1015′″that is both curved and chirped at coupling region 1040″. Thus thechirping to control the bandwidth and the focusing to reduce the size ofthe active junction area can be combined.

In another embodiment, FIG. 11 shows a top view of a sensor element 1100that is similar to sensor element 600′ of FIG. 6C. Sensor element 1100comprises multiple out-coupling gratings 1115′-1, 1115′-2 and 1115′-3 atjunction areas with a common collection area across junction region1140″. As illustrated in FIG. 11, sensor element 1100 also includesthree different pitch curved coupling gratings 1115′-1, 1115′-2 and1115′-3, as shown in the inset, are combined to form the curved grating1115. For example, each grating 1115′-1, 1115′-2 and 1115′-3 is tiltedso that the foci are at different angles from a centerline. Forsimplicity, gratings 1115′-1, 1115′-2 and 1115′-3 are shown as singlepitch gratings, but they can be chirped as well to adjust the bandwidth.These three gratings are shown overlapping in the bottom panel withthree coupling gratings 1115′-1, 1115′-2 and 1115′3 at respectivejunction areas to receive the radiation collected by each grating acrossjunction region 1140″. The details of the collection area gratinggeometry can be adjusted to optimize the collected waveguide radiationinto each of the junction areas.

FIGS. 12A-B illustrate additional collection schemes for embodiments ofdetector elements. FIG. 12A shows a top view of a sensor element 1200that is similar to sensor element 600′ of FIG. 6C. Sensor element 1200,however, comprises a crossed coupling grating 1215-1 which is shown ashaving different pitch gratings in the two orthogonal directions andlocated in a coupling region 1240′-1. For normal incident radiation thegrating will couple the same wavelength to two of the junction areas(e.g. up/down and left/right junctions). For incident radiation off ofnormal, the two pairs of junction regions will be coupled to differentwavelength radiation as described in equation (1) above. This concept isextended in FIG. 12B which shows a top view of a sensor element 1200′that is similar to sensor element 600′ of FIG. 6C. Sensor element 1200′is shown with coupling grating 1215-2 at coupling region 1240′-2.Coupling grating 1215-2 comprises four chirped and curved gratings thatare overlapped to feed input light into four junction areas withdifferent angular/spectral responses to the junction area 1240″-1,1240″-2, 1240″-3, and 1240″-4 at which respective ones of out-couplinggratings 1215′-1, 1215′-2, 1215′-3 and 1215′-4 are located. As above,the details of the coupling grating structure can be adjusted tooptimize the system response, and the final details of the structurelikely will not be a simple superposition of the individual gratingstructures. The out-coupling grating atop each junction area is adjustedto correspond to each in-coupling grating. This is not a criticaladjustment since the absorption of Si is independent of the angle ofincidence from the surface normal of the radiation. This concept is notinherently limited to four junction areas for a single collection area,but can be extended to provide additional functionality. For example,there can be four (or more) junction regions, such as at least one foreach side of the square (or other shaped) coupling area

In an alternative embodiment, a sensor element may include waveguideadd/drop filters. For example, as shown in FIG. 13, a slab waveguide1313′ may be tapered to a single mode guide 1313. As a result of theangular/spectral combinations, the spectrum in this single mode guidewill reflect particular combinations of angle and wavelength. Add-dropfilters 918, which may be based on circular resonant whispering gallerystructures, can be added to isolate various spectral regions. Theadd-drop filters 1318 may be used for providing the spectral analysis ofthe grating coupled light. The triangular section 1314′ is an adiabatictaper to funnel the light into a single mode waveguide 1313. Theadd-drop filters may be resonant whispering gallery resonators and maylead to separate detectors 1320. Because the detectors can be muchsmaller than in the previous cases, the detection speed for such anembodiment can be significantly increased. This also leads to aconcentration of the light, in effect a planar “lens” that providesenhanced signal-to-noise performance as compared with a large-areadetector. Other wavelength resonant structures, well known in the art,can be used in place of or in combination with these whispering gallerystructures.

As discussed above in connection with FIGS. 9-12B, there is opportunityfor multiplexing the coupling region to provide some separation inangular/spectral domains. The slab waveguide 1313′ can be any of theslab waveguides described above. For example, the slab waveguide maycomprise a confinement layer disposed between a first cladding layer anda second cladding layer, wherein the first cladding and the secondcladding each have a refractive index that is lower than a refractiveindex of the confinement layer, and a simple or complex dielectricgrating disposed in the first cladding layer for coupling incident lightinto the slab waveguide. Each of the add-drop filters is incommunication with a respective one of a junction region.

Additionally, sensors—such as photodetectors—that incorporate the sensorelements, such as in pixels of a 2-D pixel array, can provide detectionof a restricted angular range or detection of a wide angular range. Inan example, the restricted angular range is controlled by the use ofbaffles above the waveguide structure as in, for example, FIG. 3. Insuch a configuration, the sin θ value in equation (1) is fixed and onlyone variable remains. Thus, each coupling/junction region pair isexposed to a single wavelength for a simple grating. On the other hand,for detection of a wide angular range baffles are not used and there aredifferent values of sin θ and λ that satisfy Eq. 1. Thus, there arepotentially multiple wavelengths propagating from each coupling regionto each junction region. Accordingly, a smart lighting system may beconfigured with an arrangement of light sources, such as at least onelight emitting diode that emits light of at least one wavelengths. Inthe case of a plurality of light emitting diodes and/or a plurality ofdifferent wavelengths each wavelength may identified by the smartlighting system, for example respective identification signaturebroadcasted by at least one light emitting diode. The sensed light maybe correlated to the electronic signature by underlying electronicsportion of the smart light system. However, the sensor elementembodiment of FIG. 13 provides an alternative for providing physicalseparation of light provided by a bank of add/drop filters 1318.

Example 1A—Waveguide Detector Element

A grating coupled waveguide detector element consisting of a dielectricwaveguide over a silicon substrate with grating coupling of bothincident radiation into the waveguide and out coupling from thewaveguide into a silicon p-n junction spatially offset from the inputcoupler was constructed according to the architecture illustrated inFIG. 6A.

The parameters of the waveguide were chosen to provide a single (TE, TM)mode pair across the visible allowing the use of different gratings toadjust the individual pixel angular/wavelength coupling. For the firstexperiment a SiO₂ (n_(SiO2)˜1.5) lower cladding with a thickness of 1 μmwas used to assure low waveguide losses and to eliminate leakage intothe silicon. The Si₃N₄ guiding layer was 200 nm thick (n_(Si3N4)˜1.8)and the top cladding was adjusted to control the coupling strength. Forthe measurements reported here, a top-cladding thickness of ˜30 nm,providing a coupling length that varied from ˜2 mm (405 nm) to ˜5 mm(652 nm). The coupling grating was a photoresist grating (thickness of100 nm) with a period of 320 nm that extended over both the in andout-coupling (detector) regions. The photodiode is a standard p-ndetector with a 0.5 μm junction depth fabricated on a silicon wafer witha CMOS compatible process.

Example 1B—Experimental Results

For initial testing of the waveguide filtered CMOS compatiblephotodetector of Example 1A, lasers as light sources were used tosimplify the measurement. The fabricated devices were tested usingdiode-based, multi-mode RGB lasers of different wavelengths (652.3-,532.2- and 407.8-nm). The experimental setup consisted of the laserlight source followed by an infrared filter, polarizer, long focallength lens and an aperture to provide uniform illumination across the˜200×200 μm² coupling region and avoid any direct illumination of thejunction region.

During the measurement, the illumination angle of incident beam relativeto the grating is scanned, demonstrating the requiredangle/wavelength/polarization resolution. The measured angular spectraare wider than the theoretical predictions and show some fine structure,probably corresponding to the multi-mode character of the lasers. Forthese proof-of-principle experiments with bright sources, thephotodetector was biased at 0V so that only the intrinsic depletionregion is active. At each angle the measured photocurrent was normalizedto the laser power to compensate for power fluctuations. The angularresolution varied from ˜0.5° in the red to ˜0.25° in the blue. FIG. 14Ashows the normalized ratio of the measured photocurrent to the power oflaser for the three wavelengths.

Example 2A—Waveguide Filtered CMOS Compatible Photodetector

A waveguide was chosen to provide a single (TE, TM) mode pair across thevisible allowing the use of different gratings to adjust the individualpixel angular/wavelength coupling resonances. A photoresist couplinggrating (thickness of 100 nm) with a period of 320 nm was extendedacross the entire device including both the in- and out-coupling(detector) regions. The coupling length varied from 1.5 mm (at 405 nm)to 3 mm (at 652 nm).

Example 2 B—Experimental Results

For testing of the waveguide filtered CMOS compatible photodetector ofExample 2A, we used lasers as light sources to simplify the measurement.The fabricated devices are tested using diode-based, multi-mode RGBlasers of wavelengths 652.3-, 532.2- and 407.8-nm. The experimentalsetup consisted of the laser light source followed by an infraredfilter, polarizer, long focal length lens and an aperture to provideuniform illumination across the ˜200×200 μm2 coupling region and toavoid any direct illumination of the junction region.

Incoming light at the resonant wavelength and angle is scattered by thegrating and couples into the waveguide, propagates to the junction areaand is decoupled into the photodetector. Out-of-resonance light does notcouple into the waveguide and is either reflected or transmitted intoand absorbed in the silicon far from the photodetector active area anddoes not contribute to the photocurrent. The illumination angle of theincident beam relative to the grating was scanned with a resolution of 6arc-sec.

FIG. 14B shows the normalized ratio of the measured photocurrent to theincident power of each laser source for two sets of measurements withthe same waveguide structure but different grating pitches of 320- and380-nm. The results for the two pitches are vertically offset forclarity. The measured angular spectra are slightly wider than thetheoretical predictions (discussed below) and show some fine structure,probably corresponding to the multi-mode character of the lasers. Thelinewidth is a convolution of the scattering/absorption propagationlosses of the bare (no grating) waveguide and the spectral widthcorresponding to the width of the coupling area (the smallest ofphysical dimension of the grating, the illumination spot size, or thecoupling length). In these experiments, the laser spot size(˜200 μm) isthe major contribution to the observed linewidth.

FIG. 14C shows wavelength vs. coupling angle for different gratingperiods. Multiple orders of the grating are shown. (e.g. the notation800/2 refers the the second order of a 800 nm pitch grating). Theexperimental points are indicated. FIG. 14D shows wavelength vs. gratingperiod at a fixed angle. Both forward and backward scattering regimesare indicated. For both figures the solid lines are TE modes and thedotted lines are the TM modes.

A High-Responsivity Blue-Enhanced CMOS Compatible Photodetector UsingHoneycomb Structure

Improved responsivity and detection of visible light colors (includingblue) is one of the important specifications of light sensor for smartlighting. Since the energy of blue photons is the highest in the visiblespectrum, the responsivity of photodetectors for blue photons isfundamentally the lowest (proportional to λ). That is, above the siliconbandgap energy (BG), the responsivity scales as λ/BG for a fixed quantumefficiency since only one electron-hole pair is generated for eachphoton absorption, independent of the wavelength. Furthermore the highabsorption coefficient of silicon in the blue spectral region leads to alow quantum efficiency for conventional p-n junction detectors where thedepletion region is buried some distance into the silicon. FIG. 15 showsthe ideal (fundamental limit, e.g. the λ/BG response) and practicalresponsivities, which deviate from the ideal response at shorterwavelength, confirming that blue photons suffer from lowered sensitivityrelative to longer wavelength photons.

Blue-enhanced photodetectors are available commercially; however, theirfabrication requires a non-standard PIN process, which makes it costinefficient. Because the absorption coefficient of blue photon is high,they normally get absorbed very close to the surface of thephotodetector (at a 400 nm wavelength, the photon absorption length is˜100 nm). To enhance the quantum efficiency of blue photons, one mustbring the depletion region as close as possible to the surface. This ispractically very hard to fabricate, since the p or n region on thesurface needs a minimum thickness. However, at the edge of a detectorwhere for example a n-well is fabricated in a p-region, the depletionregion already touches the surface. Therefore, the edge of aphotodetector presents the highest responsivity. Experiments using alaser beam scanning technique on a simple, large-area planar p-njunction device, as illustrated in FIG. 16, confirm that the edge of aphotodetector presents the highest responsibility. For example, there isa 22% overshoot in responsivity (photocurrent) when the laser beamreaches the edge of the detector (the direction of the laser beam isindicated by the right-pointing arrow in the inset). This enhancement isprobably understated since it is averaged over the beam size, whichlimits the resolution and the peak enhancement.

Accordingly, in an embodiment there is a CMOS-compatible photodetectorhaving structure that comprises a p-n junction. The edge portions of thep-n junction of the structure can be utilized to improve the detectorresponsivity. The structure has the appearance of a honeycomb,containing a large number of edges within the active photodetector areaand an enhanced p-n junction area (depletion region volume).

FIGS. 17A-17C illustrate top and side view (layout and cross section) ofa conventional p-n detector 1700 having planar junction structure. Asshown by the cross-sections of FIG. 17B and FIG. 17C taken along dashedline A-A′ and B-B of FIG. 17A, respectively, a planar n-type layer 1701is disposed over a planar p-type layer 1703. The two views show thatacross the device, the p-type and n-type layers are planar across aselected width of the device (i.e., the two views are identical).

Meanwhile, FIGS. 18A-18C illustrate a top and side view (layout andcross section) of a honeycomb p-n detector structure 1800 of anembodiment that utilizes the junction edges to enhance the detectorresponsivity. The honeycomb p-n detector structure comprises a a firstsemiconductor layer 1803 and a second semiconductor layer 1801. Thefirst semiconductor layer 1803 may be doped with a first carrier type(for example, p-type dopant) and may include a plurality of posts 1803′.The second semiconductor layer 1801 may be doped with a second carriertype (for example, an n-type dopant) and may be configured with aplurality of holes extending through the second semiconductor layer. Theholes may be arranged as an array of holes. The hole-containing patternof the second semiconductor layer 1803 may be viewed as a plurality ofinterconnected open cells. Accordingly the holes may comprise the openportion of the open cells. In an embodiment the open cells may have anyshape including any fractal shape.

The posts 1803′ may extend through a corresponding one of the pluralityof holes in a honeycomb pattern. In an embodiment, the honeycomb patterncomprises a plurality of edge portions, each of the plurality of edgeportions comprising a respective one of a depletion region area. Thehoneycomb pattern, therefore, comprises a single p-n junction.

Two cross sections, corresponding to cuts labeled A-A′ and B-B′ areshown in FIGS. 18B and 18C, respectively. Cut A-A, through the center ofthe second semiconductor 1801's holes, is shown in FIG. 18B with posts1803′ extending through the holes in the second semiconductor layer1801. Cut B-B′, to the side of the second semiconductor 1801's holes, isshown in FIG. 18C with second semiconductor layer 1801 disposed on thefirst semiconductor 1803. The portion of the semiconductor layers 1801and 1803 along cut B-B′ are configured as layers 1701 and 1703 in theconventional detector design of FIG. 18C.

While FIG. 18A shows a honeycomb structure having a square honeycomblattice, different configurations are possible, so long as all p-regionsand all n-regions are electrically continuous. The more complexstructure of the depletion region in the honeycomb photodetectorenhances the responsivity across the visible. As discussed above, theblue response is enhanced by bringing the depletion region up to thesurface of the silicon. For longer wavelengths—where the absorptiondepth is much further into the material—the enhanced volume of theconvoluted depletion region, in comparison to the simple planar junctionstructure, leads to an enhanced response. The extended depletion regionvolume also corresponds to increased dark current and therefore toincreased receiver noise. Many degrees of freedom are available toexploit in optimizing this photodetector. Such degrees of freedominclude, but are not limited to the size and geometry of the honeycombcells, the depth of the cells, the doping concentrations, etc. Fordifferent uses, e.g. high speed, high responsivity, low noise, therewill be a different optimum. Each of these variants is incorporatedherein.

The fabrication of the honeycomb detector does not require anyadditional mask or fabrication steps than a conventional planarphotodetector. The honeycomb cells can be easily implemented bymodifying the layout of the active region. The doping can be by anywell-known doping technique such as diffusion or ion-implantation andannealing. Ion-implantation is advantageous for small honeycombgeometries and for high depth to planar dimension aspect ratios. Any oneof the p-n junctions of the embodiments disclosed herein may beconfigured as a p-n honeycomb structure such as the p-n honeycombstructure 1800.

In other words, in an embodiment there is a CMOS-compatiblephotodetector comprising a first semiconductor layer in contact with asecond semiconductor layer to form a p-n junction, wherein thephotodetector comprises a plurality of edge portions within an activephotodetector, each of the plurality of edge portions corresponding to adepletion region that extends in a direction perpendicular to the edgeportion into both the p- and n-regions of the semiconductor, wherein theplurality of edge portions enhance detector responsivity, and furthercomprise a honeycomb structure.

In an embodiment there is a smart lighting system that comprises atleast one of the 2-D arrays and/or CMOS compatible photodetectorembodiments described herein. A 2-D sensor array and/or CMOS compatiblephotodetector of the embodiments can be in electrical communication withelectronics. In an embodiment, the 2-D sensor array and/or CMOScompatible photodetector may be bump bonded to a silicon chip with theelectronics. In an embodiment, 2-D sensor array and/or CMOS compatiblephotodetector may have the electronics for reading out the “pixelvalues” incorporated therein. The 2-D sensor array and/or CMOScompatible photodetector can have a spectral range of about 20 nm toabout 50 nm over 7 to 21 spectral ranges across the 380 nm to 700 nmvisible spectrum. In other embodiments there can be 420 detectors with˜1 nm spectral resolution to cover the visible The 2-D sensory arrayand/or CMOS Compatible photodetector can be configured to receive 10 to13 angular samples of light at a polar angle of −60° to 60° (f/1.75) atabout 15° intervals, and 8 angles along 3 to 4 azimuthal anglesseparated by 120°. The 2-D sensory array and/or CMOS Compatiblephotodetector of at least one embodiment described above can furthercomprise about 150 pixels. The 2-D sensor arrays of the embodiments maybe included in a CMOS compatible photodetector, with each pixel having arestricted angular acceptance of about 10° in both polar and azimuthalangles. For example, in a configuration where angular acceptance of eachpixel is constrained, only one wavelength is coupled to each junctionarea and there is no need for a wavelength separation.

In an embodiment there is a method of using one or more of the 2-Dsensor arrays and/or the CMOS compatible photodetectors describedherein. For example, in use, light generates surface plasma waves boundto a metal-dielectric interface of the sensor. Alternatively, the lightgenerates waveguide modes confined by a dielectric stack of thewaveguide. Accordingly, the method may include providing a 2-D sensorarray. The 2-D sensor array may include any of the sensor elementsdescribed herein. For example, the 2-D sensor array may include asemiconductor substrate comprising a plurality of pixels, which may bedisposed on the substrate. Each of the plurality of pixels may compriseat least one coupling region and at least one junction region, a slabwaveguide structure disposed on the semiconductor substrate that extendsfrom the coupling region to the junction region, and at least one p-njunction in the junction region. A localized semiconductor layer mayform the at least one p-n junction with the semiconductor substrate inthe junction region. For example, the localized semiconductor layer mayhave a first conductivity type (for example, doped with a dopant havinga first conductivity type such as p or n-type) and the substrate mayhave a second conductivity type (for example, doped with a dopant havinga second conductivity type opposite that of the first type). The slabwaveguide may include a confinement layer disposed between a firstcladding layer and a second cladding layer, wherein the first claddingand the second cladding each have a refractive index that is lower thana refractive index of the confinement layer. The pixels may furthercomprise at least one grating disposed in the slab waveguide. The atleast one grating may include a grating period. The method may alsoinclude coupling incoming light into the slab waveguide at the couplingregion, propagating the light to the region over the junction area,decoupling the light such that it enters the junction region, andconverting the light into at least one electron-hole pair, wherein theincoming light comprises at least one modulated waveform. Theelectron-hole pair may be collected, such as by electronics incommunication with the 2-D sensor array such as electroncs of a smartlighting system that includes the 2-D sensor array in electroniccommunication with a controller which in turn controls at least one,such as a plurality, of light sources.

The 2-D sensor arrays and/or the CMOS compatible photodetectorsdescribed herein comprise sensors, which receive optical input (e.g., alight field), and convert it into a meaningful electrical output. In anembodiment, the electrical output can be representative of a series ofintensity vs. wavelength plots at different angles of incidence, orequivalently intensity vs. angle of incidence plots at differentwavelength.

FIG. 19A shows the spectral response of a conventional p-n detector(such as that of FIG. 17A) and a honeycomb p-n detector of theembodiments, such as that of FIG. 18A). The honeycomb detectordemonstrates significant improvement in responsivity compared with theconventional detector. FIG. 19B shows the photocurrent increase of thehoneycomb p-n detector relative to the conventional p-n detector.

While the invention has been illustrated respect to one or moreimplementations, alterations and/or modifications can be made to theillustrated examples without departing from the spirit and scope of theappended claims. In addition, while a particular feature of theinvention may have been disclosed with respect to only one of severalimplementations, such feature may be combined with one or more otherfeatures of the other implementations as may be desired and advantageousfor any given or particular function.

Furthermore, to the extent that the terms “including”, “includes”,“having”, “has”, “with”, or variants thereof are used in either thedetailed description and the claims, such terms are intended to beinclusive in a manner similar to the term “comprising.” As used herein,the phrase “one or more of”, for example, A, B, and C means any of thefollowing: either A, B, or C alone; or combinations of two, such as Aand B, B and C, and A and C; or combinations of three A, B and C.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

What is claimed is:
 1. A 2-D sensor array, comprising: a plurality ofpixels including at least a first pixel and a second pixel, wherein eachof the first and second pixels comprise: a slab waveguide portion, asingle mode waveguide portion, an adiabatic taper portion for funnelingincident light from the slab waveguide portion into the single modewaveguide portion, and a plurality of resonant add-drop filters formedsubstantially adjacent to the single mode waveguide portion, wherein theslab waveguide comprises: a confinement layer disposed between a firstcladding layer and a second cladding layer, wherein the first claddingand the second cladding each have a refractive index that is lower thana refractive index of the confinement layer, and a grating disposed inthe first cladding layer for coupling incident light into the slabwaveguide.
 2. The 2-D sensor array of claim 1, wherein the first pixel'sgrating has a first grating period and the second pixel's grating has asecond grating period, and wherein the first grating period is differentthan the second grating period.
 3. The 2-D sensor array of claim 1,further comprising at least one detector, wherein each of the pluralityof resonant add-drop filters is in communication with a respective oneof the at least one detector.
 4. The 2-D sensor array of claim 1,wherein each add-drop filter is configured to drop a first wavelengthband.
 5. The 2-D sensor of claim 4, wherein at least one of theplurality of add-drop filters is arranged to transmit the firstwavelength band to a detector.
 6. The 2-D sensor of claim 1, whereineach add-drop filter is configured to transmit a second wavelength bandto a subsequent one of the add-drop filters, thereby providing aspectrum of the light in the waveguide.
 7. The 2-D sensor array of claim1, wherein the 2D array is configured to receive incident light over afraction of 2πsteradians.
 8. The 2-D sensor array of claim 1, whereinthe plurality of resonant add-drop filters comprise circular resonantwhispering gallery resonators.
 9. The 2-D sensor array of claim 1,wherein the adiabatic taper portion comprises a tapered cross sectionthat extends from a first end of the adiabatic taper portion to a secondend of the adiabatic taper portion, the second end disposed adjacent thesingle mode waveguide portion.
 10. A 2-D sensor array, comprising: asemiconductor substrate, a plurality of pixels disposed on thesemiconductor substrate, wherein each of the plurality of pixelscomprise: at least one coupling region and at least one junction region;a slab waveguide structure disposed on the semiconductor substrate andextending from the at least one coupling region to the at least onejunction region, and comprising a confinement layer disposed between afirst cladding layer and a second cladding layer, wherein the firstcladding and the second cladding each have a refractive index that islower than a refractive index of the confinement layer; and at least onecoupling structure disposed in the coupling region and within the slabwaveguide, the coupling structure comprising at least two materialshaving different indices of refraction, and arranged as a gratingdefined by a grating period, wherein the junction region comprises a p-njunction in communication with electrical contacts for biasing andcollection of carriers resulting from absorption of incident radiation,and wherein the at least one coupling structure comprises a firstdielectric grating positioned in the coupling region for couplingincident light into the slab waveguide and a second dielectric gratingpositioned in the slab waveguide region over the junction region forcoupling light from the waveguide into the junction region.
 11. The 2-Dsensor array of claim 10, wherein the slab waveguide comprises a modalindex of between about 1.5 to about 2.3.
 12. The 2-D sensor array ofclaim 10, wherein each of the first and the second dielectric gratingscomprise a plurality of grating teeth, and wherein the second dielectricgrating's coupling strength is greater than that of the first grating.13. The 2-D sensor array of claim 10, wherein the first dielectricgrating comprises a chirped grating in the coupling region and thesecond grating comprises a fixed and chirped grating in the junctionregion.
 14. A photodetection system comprising a controller; at leastone photodetector in electronic communication with the controller; and aplurality of light sources configured to emit a plurality of wavelengthsin the visible spectrum, wherein the system is configured to provide asuitable identification modulation for each of the plurality ofwavelengths such that each of the plurality of wavelengths comprises arespective identification signature broadcasted by each of the pluralityof light sources.
 15. The photodetection system of claim 14, wherein theplurality of light sources comprises a plurality of light emittingdiodes, a plurality of lasers, or a combination of a plurality of lightemitting diodes and a plurality of lasers.
 16. The photodetection systemof claim 14 wherein the photodetector is configured to generate a signalcorresponding to at least one of the plurality of different wavelengths,and wherein the controller is configured to accept the signal andcompare it to an identification signature of at least one of theplurality light sources.
 17. The photodetection system of claim 14,wherein the photodetector comprises a plenoptic detector comprising anarray of pixels including at least a first pixel and a second pixel,wherein each of the first and second pixels comprise: a slab waveguideportion, a single mode waveguide portion, an adiabatic taper portion forfunneling incident light from the slab waveguide portion into the singlemode waveguide portion, and a plurality of resonant add-drop filtersformed substantially adjacent to the single mode waveguide portion,wherein the slab waveguide comprises: a confinement layer disposedbetween a first cladding layer and a second cladding layer, wherein thefirst cladding and the second cladding each have a refractive index thatis lower than a refractive index of the confinement layer, and a gratingdisposed in the first cladding layer for coupling incident light intothe slab waveguide.
 18. The photodetection system of claim 17, whereineach add-drop filter is configured to drop a first wavelength band. 19.The photodetection system of claim 18, wherein at least one of theplurality of add-drop filters is arranged to transmit the firstwavelength band to the photodetector.
 20. The photodetection system ofclaim 14, wherein the photodetector comprises a CMOS-compatiblephotodetector, the CMOS-compatible photodetector comprising: a firstsemiconductor layer doped with a first carrier type and comprising aplurality of posts, and a second semiconductor layer doped with a secondcarrier type configured with a plurality of holes extending through thesecond semiconductor layer, wherein at least one of the posts extendsthrough a corresponding one of the plurality of holes in a honeycombpattern, and wherein the honeycomb pattern comprises a plurality of edgeportions, each of the plurality of edge portions comprising a respectiveone of a depletion region area.